1. Technical Field
The invention relates to a device that uses a plasma, for example, a plasma etching device. More particularly, the invention relates to a plasma ignition device, e.g. an igniter, for generating a low pressure plasma.
2. Description of the Prior Art
In recent years, the so-called dry process, for example in which a semiconductor wafer is etched or a thin film is formed using plasma generated at a low pressure, has become significant and indispensable to the manufacture of highly functional and highly integrated semiconductor devices, e.g. ultra-LSI. Plasma etching with a plasma etching device involves active seeds, such as ions that are generated when a chemically active gas (referred to as .sup.'etching g.about.5YI below) is discharged in a plasma state. These active seeds interact with a solid material that is to be etched, such as a semiconductor wafer, such that volatile reaction products are formed and released in a vapor phase.
In a typical prior art plasma etching device, the upper opening and the lower opening of the side wall that comprises the vacuum chamber are each closed with an end plate. The upper end plate functions as an anode. A suscepter, which functions as a cathode, is arranged over the lower end plate. A matching circuit and a high frequency bias power source are connected between the anode and the cathode. A coil is also arranged around the vacuum chamber. The matching circuit and high frequency power source are connected to the coil at both ends.
When a high frequency is applied to the coil in such a plasma etching device, a plasma is generated as a result of high frequency coupling to an etching gas introduced into the vacuum chamber. A bias is then separately applied between the anode and the cathode to accelerate the ions, such that a semiconductor wafer mounted over the cathode is etched by the plasma ions.
When the coil to which a high frequency is applied is used to generate a plasma as described above, a portion of the plasma does not proceed toward the object, such as a semiconductor wafer, due to the electric field the coil has generated. Rather, a portion of the plasma proceeds to the side wall of the vacuum chamber, hits the wall of the vacuum chamber, and etches the vacuum chamber wall. Unfortunately, when the voltage applied to the coil is reduced to control such behavior of the plasma, a plasma is not generated in the vacuum chamber if the vacuum chamber is filled with a low pressure etching gas. Filling the vacuum chamber with a high pressure etching gas is not an acceptable alternative with respect to the manufacture of state of the art highly functional and highly integrated semiconductor devices.
It would therefore be advantageous to offer an ignition device for low pressure plasma that can generate low pressure plasma in a vacuum chamber.